In recent years, one-dimensional nanowires have attracted much research interest due to their very large aspect ratio and surface area conferring them with unique magnetic, electronic, and optoelectronic properties. For instance, Au, Ag, Cu and semiconductor nanowires show unique electron transport capabilities, not observed in the corresponding bulk materials; and ferromagnetic nanowires such as Ni, Co and Fe-based nanowires are candidates of choice for magnetic field sensors.
Known methods enabling the fabrication of such nanowires include, for instance, NUR Ubaidah Saidin et al. (Adv. Mat. Res. Vol. 364 (2012) pp. 303-307), which discloses a process developed to fabricate anodic aluminium oxide (AAO) templates suitable for the fabrication of nanowire arrays. In this reference, an anodization process was used to fabricate an AAO template with pore diameters ranging from 15 nm to 30 nm. Electrodeposition of parallel arrays of high aspect ratio nickel nanowires was demonstrated using these fabricated AAO templates.
However, a potential issue for such template-based methods is that the higher the aspect ratio of the nanowires, the more they tend to collapse during their separation from the template. This collapse is an aggregation of the free extremities of the nanowires, thereby forming separate bundles of nanowires. Without being bound by theory, this collapse is believed to be due to the mutual attraction between those nanowires and to the surface tensile force in the drying process. An example of this collapse is illustrated in FIGS. 12 and 13.
One approach that may help to avoid this collapse is mentioned in Yongqi Liang et al. (J. Am. Chem. Soc., 2004, 126 (50), pp 16338-16339) where a supercritical drying technique is combined with AAO. This technique is however relatively expensive as it involves advanced equipment. Furthermore, this technique is not easily adaptable to large substrate sizes and to industrial-scale manufacturability. For example, this technique does not appear to be practically usable for large area foil processing such as roll-to-roll (RtR) processing.
There is therefore a desire new methods enabling the fabrication of a cluster of non-collapsed nanowires while avoiding known drawbacks of conventional techniques